The present invention relates to a secondary battery, and, more particularly, to a separator having a protrusion which is obtained by modifying the shape of the conventional separator and that also functions as an upper insulator, and a cylindrical secondary battery employing the same.
FIG. 1 is a sectional view of a general cylindrical secondary battery, and FIG. 2 is a sectional view showing only the cap assembly of the cylindrical secondary battery. As shown in FIGS. 1 and 2, a cylindrical secondary battery has a structure in which a roll of cathode and anode plates 16 and 17 with a separator 18 therebetween is placed in a cylindrical metal can 10. Also, upper and lower insulators 15 and 20 for supporting and fixing the roll and for insulating the roll from the bottom of the metal can 10 or cap portion are installed at the upper and lower portions of the roll. A cap 11 having a rubber-vent 12 therein and a cap cover 13 are installed on the upper insulator 15. Cap cover 13 is electrically connected to the cathode plate 16 via a tab 21. Also, a gasket 14 is installed around the sealing portion between the cap 11 and the cap cover 13, supporting and fixing the cap and the cap cover 13.
The assembly process of the cylindrical secondary battery having the above structure is as follows. First, the lower insulator 20 is inserted to the bottom of the cylindrical metal can 10 parallel to the bottom surface, and then the roll of cathode and anode plates 16 and 17 having the separator 18 therebetween is inserted therein. Thereafter, a flat upper insulator 15 having a through hole in the center is put on the roll. Next, a beading process is performed and then a gasket 14 is inserted. The gasket 14 prevents leakage of electrolyte, thereby protecting the battery. Then, a cap assembly including the cap 11, the cap cover 13 and the rubber-vent 12 is seated on the upper end of the metal can. Then, the metal can 10 is crimped and pressed to complete the cylindrical secondary battery.
However, in the manufacture of the cylindrical secondary battery, since the flat upper insulator having a through hole in the center is formed of a hard synthetic resin such as polyvinyl chloride (PVC) or polypropylene (PP), the roll of anode and cathode plates may be damaged by the inner wall of cylindrical metal can when the metal can is crushed during the beading, crimping, and pressing processes, which lowers the performance of a resultant battery.